The denomination “egg” refers primarily to the chicken egg. There are also several types of edible eggs laid by female fish and reptile birds: ducks eggs, quail eggs, goose, turkey, partridge and fish eggs.
The egg is a common ingredient that is part of many dishes around the world. More than 1 000 billion eggs are consumed per year worldwide, about 145 eggs per inhabitant per year.
That is to say that it is an essential component of our diet. Most people don’t know many facts about eggs and have a lot of false ideas concerning its place in our alimentation.
The egg is an organic body of variable dimensions whose initial objective is to assure the oviparous species the reproduction of their species.
It provides food reserves to ensure the development of the embryo. These reserves offer a unique composition of nutrients.
Through this article, we will try to expose the composition of the eggs and to detail their nutritional value with their nutrition facts. We will also answer all your questions while making sure to demystifying conventional wisdom and unravelling the most common misconceptions about this popular food choice.
Let us start with the macroscopic composition of the egg: It consists of four main parts, the shell, the membranes, the white and the yellow:
The shell of the egg
The shell of an egg represents about 10% of its total weight. It is a porous and fragile shell.
It has many tiny orifices preserving, but also letting through moisture, odors and air. An average egg has between 6,000 and 8,000 pores on its surface. The small holes in the shell allow the chicks to breathe before the hatching of the egg.
The shell is also a barrier against microbes.
Very often, producers very often coat the shell with an odorless layer of oil to partially block the pores to minimize moisture loss; this operation prevents the penetration of odors and prolongs the freshness.
The breed of hens determines the color of the shell. It is a genetic factor with absolutely no effect on the flavor and nutritional value of eggs. The thickness of the shell depends on the feeding of the hens and hereditary factors.
The albumen more commonly named “egg white”, constitutes two-thirds of the egg. It consists of 87% water and 12% albumin (Protein family). The white is transparent and viscous; it is soluble in water.
The egg white coagulates and solidifies between 62 and 65 degrees centigrade and takes on intense white color.
Yellow or yolk represents 30% of the egg. It consists of several superimposed layers of yolk, of a light yellow to dark yellow color. The yolk is surrounded by the vitelline membrane (transparent membrane). Yellow is divided between 50% solids and 50% liquids; it contains 16% protein and 30% fat.
The lipids of yellow contain “lecithin”, an emulsifying substance that plays a critical role in the preparation of pastries, creams and pasta. Lecithin, made of nitrogen and phosphorus, links fat and water, thus promoting the emulsions, the texture, the softness and the conservation of the culinary preparations.
The color of an egg yolk varies according to the diet of the hen, so a diet rich in corn gives a darker yellow and a diet rich in wheat produces very pale yellows.
The yolks of unfertilized eggs present as a small pale spot of irregular shape, it is the germinal disc.
The yellow alone coagulates between 65 and 70 degrees centigrade, diluted in a liquid, the yellow coagulates between 80 and 85 degrees centigrade.
Membrane and inner tube:
A shell membrane (consisting of 2 or 3 thin layers of protein fibers) adheres to the shell and serves as protection against mold and bacteria.
Initially, the egg is entirely inhabited by its contents. During the thermal shock between the internal temperature of the hen and the outside temperature, the egg, while contracting, forms a pocket of air called “air chamber”.
The size of the air chamber depends on the storage conditions, i.e. the degree of humidity, the surrounding heat and the level of evaporation: a loss of moisture or dehydration causes an increase in the volume of the air chamber.
The air chamber thus provides a valuable indication of the freshness of the egg, the larger it is, the older the egg. A larger air chamber, therefore, indicates an egg stored in fresh and cold enough conditions.
Eggs Nutrition Facts
Recent scientific evidence suggests that the egg is a food of choice and that consumption of one egg per day, even for people with high blood cholesterol, is advisable. The egg is nutritious, versatile and offers excellent and essential nutrients at a low cost.
The yolk contains two powerful antioxidants from the Carotenoids family: Lutein and Zeaxanthin. Moreover, these two compounds confer the color to the yolk of the egg. Carotenoids, substances similar to vitamin A, are antioxidants known to help prevent age-related diseases, such as cataracts, macular degeneration, cardiovascular diseases and certain cancers. These antioxidants neutralize or reduce free radicals in the body and thus limit cell damage. Observational studies indicate consumption of Lutein-rich foods, such as eggs, may help prevent age-related macular degeneration, a leading cause of blindness in people aged 65 and older, and to reduce the risk of cataracts. The possible role of Carotenoids in the prevention of cardiovascular disease (CVD) is to reduce the oxidation of LDL-cholesterol (“bad cholesterol”) and to reduce plaque formation in the artery walls.
Finally, Carotenoids may reduce the risk of certain cancers. Data from a prospective study showed that the higher the intake of Lutein and Zeaxanthin, the lower the risk of breast cancer in peri-menopausal women.
The egg is composed of proteins of high biological value. Proteins are used primarily to form, repair and maintain tissues, such as skin, muscles and bones, in good condition. They are also used for the formation of digestive enzymes and hormones.
The proteins contained in the egg are called complete because they provide the nine amino acids essential to the body, and this, in optimal proportions. Indeed, the protein quality of the egg is such that it is used as a reference food to assess the quality of other dietary proteins.
Note that amino acids are said to be essential when the body cannot produce them. They must come from food. About 60% of the egg proteins are found in the white while the remaining 30% is in the yolk.
The egg is an excellent source of Choline, a compound that plays a vital role in the development and functioning of the brain, primarily the center of memory.
Choline is found mainly in the yellow part of the egg. Choline is essential during embryonic development since during pregnancy and lactation, low intake of this molecule may have long-term effects on the development of the child’s brain.
An animal study has shown that supplementation with Choline, during embryonic development in rats or immediately after birth, would improve cognitive function and, by extension, attention and memory.
In a study of pregnant women with low folic acid intakes, authors also reported that mothers with the lowest Choline intake were four times more likely to give birth to a child with neural tube defects than those with the highest intakes, regardless of folic acid intakes.
The egg is an excellent source of selenium. This mineral works with one of the main antioxidant enzymes, preventing the formation of free radicals in the body. It also helps to convert thyroid hormones into their active form.
The egg is a good source of vitamin B2. This vitamin is also known as riboflavin. Like vitamin B1, riboflavin plays a role in the energy metabolism of all cells. Besides, it contributes to the growth and repair of tissues, the production of hormones and the formation of red blood cells. Most of the riboflavin is found in egg white.
The egg is a good source of vitamin B12. This vitamin works together with folic acid (vitamin B9) for the production of red blood cells in the blood. It also watches over the maintenance of the nerve cells and the cells making the bone tissue.
The egg is a source of phosphorus, which plays a vital role in the formation and maintenance of healthy bones and teeth. Besides, it participates among other things in the growth and regeneration of tissues and helps to maintain the pH of the blood. Finally, phosphorus is one of the constituents of cell membranes.
The egg is a source of zinc. Zinc is involved in immune responses, the production of genetic material, taste perception, scarring and fetal development. Zinc also interacts with the sexual and thyroid hormones and participates in the pancreas in the synthesis, storage and release of insulin.
The egg is a source of Pantothenic acid. Also known as vitamin B5, Pantothenic acid is part of an essential coenzyme that allows us to utilize the energy present in the foods we consume adequately.
He also participates in several steps in the synthesis of steroid hormones, neurotransmitters (messengers in nerve impulses) and hemoglobin.
The egg is a source of folate. Folate (vitamin B9) is involved in the production of all body cells, including red blood cells. This vitamin plays an essential role in the production of genetic material (DNA, RNA), in the functioning of the nervous system and the immune system, as well as in the healing of wounds.
As it is necessary for the production of new cells, adequate consumption is essential during periods of growth and for the development of the fetus.
The egg is a source of vitamin A. This vitamin is one of the most versatile, playing a role in several functions of the body. It promotes, among other things, the growth of bones and teeth. It keeps the skin healthy and protects against infections. Also, it plays an antioxidant role and promotes good vision, especially in the dark. Most vitamin A is found in egg yolk.
The egg is a source of vitamin D. Vitamin D interacts closely in the health of bones and teeth, making available calcium and phosphorus in the blood, among other things for the growth of bone structure. Vitamin D also plays a role in the maturation of cells, including those of the immune system. Most vitamin D is also found in egg yolk.
The egg is a source of vitamin E. As a major antioxidant; vitamin E protects the membrane that surrounds the body’s cells, especially red blood cells and white blood cells (immune system cells).
Omega-3 (For Omega-3-enriched eggs)
Omega-3 eggs are identical to conventional eggs regarding total fat and cholesterol content. Only the omega-3 polyunsaturated fatty acid content of one differentiates it from the other.
Eggs enriched in omega-3 are produced by adding to the diet of the hen of the flaxseed. The latter is rich in alpha-linolenic acid (ALA), a type of omega-3 fatty acids.
An omega-3 egg covers 25% to 30% of our ALA needs, which may represent a supplement to these fatty acids that have a major role in the prevention of cardiovascular diseases.
Through the previous section, we conclude that eggs are a top choice and incredibly rich foods of our diet. However, some precautions are required regarding their use to enjoy their benefits without getting some side effects.
The allergies :
Eggs constitute, along with milk, peanuts and crustaceans, one of the main causes of food allergies. Egg allergy is usually caused by the reaction of the immune system to one of the protein fractions contained in the egg white. However, in some people, it is the proteins contained in the yolk that cause the allergy.
Fortunately, in the majority of children with egg allergy, this side effect disappears after the age of five. However, when the allergy is severe, it is likely to last for life. As a precautionary measure, egg white should not be introduced into the child’s diet before the age of one year.
The most common symptoms of egg allergy affect the gastrointestinal system (vomiting, diarrhea), the respiratory system (asthma, bronchitis) and can also often cause skin problems (eczema).
Toxic infections :
Egg safety is of primary importance given the potential for contamination by bacteria or viruses (like salmonella and H5N1). The FAO estimates that the compliance rate of egg products inspected was